The present invention relates to a composite material and a method for production of the same.
A composite material is a composition aggregate in which a plurality of materials are macroscopically mixed, and thus complementary employment of mechanical characteristics of each material enables a demonstration of characteristics that was not realized by the material independently. Fundamentally, it is a technique that combines materials and materials together, and has various combinations based on matrixes, reinforcing materials (dispersing materials), purposes of use, and cost.
Among them, a metal matrix composite material, or an intermetallic compound matrix composite material is a composite material in which metals, such as Al, Ti, Ni, and Nb, or intermetallic compounds, such as TiAl, Ti3Al, and Al3Ti, NiAl, Ni3Al, Ni2Al3, Al3Ni, Nb3Al, Nb2Al, and Al3Nb, are used as a matrix, inorganic materials, such as ceramics, are used as a reinforcing material to be composite material materialized. Accordingly, taking advantage of the characteristics of being lightweight and having a high strength, application of a metal matrix composite material, or an intermetallic compound matrix composite material, for many fields, such as universe and aviation industry field are now promoted.
Besides, in general an intermetallic compound matrix composite material has a fault that fracture toughness is low as compared with a metal matrix composite material, but on the other hand, based on mechanical and physical characteristic of a matrix, it also has characteristic superior in heat-resistant characteristics, abrasion resistant characteristics, and has low thermal expansion and high rigidity.
A method for production of an intermetallic compound matrix composite material includes a method in which an intermetallic compound powder is beforehand produced by a mechanical alloying (MA) method etc., and subsequently it is molded with fiber and/or particles used as a reinforcing material etc. under a high temperature and a high-pressure condition using a hot pressing (HP), or hot isostatic pressing (HIP).
A problem in conventional methods of producing an intermetallic compound matrix composite material is as follows: in order to produce a densified intermetallic compound matrix composite material, a high temperature and a high pressure are required to be applied and an intermetallic compound should be sintered to obtain a densified composite material using powder metallurgical production methods, such as HP method and HIP method. Other problems are that a pretreatment process is required, performance and scale of a producing apparatus are restricted, and a production of the composite material with a large size or complicated shape is extremely difficult, simultaneously near net shape method in consideration of the shape of final products cannot be applied, and thereby, machining processing is required in later processes.
Besides, there is a problem that synthesis of an intermetallic compound powder by MA etc. is beforehand required as a pretreatment process, and many stages are required in the producing process, thereby the process turns to be complicated. Therefore, as mentioned above, since a conventional method for production of an intermetallic compound matrix composite material is a method for production conducted under a high temperature and a high-pressure condition with a necessity of the processes over many stages, it is a method for production requiring very high cost.
There have been generally known, as a method for producing an intermetallic compound matrix composite material, techniques for diffusion-bonding a sheet-like or foil-like metal and a fiber-like or granular ceramics under a high pressure such as HP method, HIP or the like being classified as a solid state fabrication method, and said powder metallurgical production methods wherein metallic powder is used. Any of the above-mentioned solid state fabrication methods and liquid state fabrication methods requires high temperature and high pressure. Additionally, there is known, as a liquid state fabrication method, a method wherein a composite material is forcedly produced by compounding a metal and a ceramic utilizing a mechanical energy such as a high pressure or the like, such as high pressure infiltration method, melt forging method or the like. Furthermore, any of thus produced composite materials has always a simple shape, such as a plate-like or a disk-like one. It also requires plasticity processing, mechanical processing or the like to obtain a finished product. Therefore, those methods are quite expensive ones since the processing cost is quite high due to the co-presence of ceramic phase in the product.
There is proposed, as the related technique for solving such problems, especially a method for providing a composite material at relatively lower cost, a method for producing a metal matrix composite material which does not require a high pressure for production, not likewise the conventional synthetic process. For example, there is proposed a method for producing a metal matrix composite material having metals, such as an aluminum (Al), as a matrix, in which a formed body comprising reinforcing materials having a minute piece shape and minute pieces having a getter effect of oxygen and nitrogen, such as titanium (Ti), is formed, and then immersed into molten metals, such as aluminum (Al), is disclosed as a method utilizing a liquid phase process in which molten metal is infiltrated under a pressureless condition (See Japanese Patent No. 3107563, for example).
However, according to the above described method, it is necessary that a pressure is applied to mixed powder in the method to produce a formed body, and that the formed body is soaked in a molten metal, such as aluminum (Al), and therefore, the formed body should have a certain strength durable for handling during that period. Accordingly, it is required to use a high pressure at the time of forming the formed body. Thus, the shape of the product to be produced is limited. Besides, the composite material obtained is limited to metal matrix composite materials having a matrix formed from metal containing less amount of an intermetallic compound therein. Furthermore, since a formed body expands due to an exothermic reaction between titanium (Ti)—aluminums (Al), immersion of the formed body into a molten metal reduces a volume fraction of a reinforcing material, leading to difficulty in producing a composite material with a higher reinforcing material volume fraction, and in proving a composite material having controlled material characteristics inclusive of a higher mechanical strength.
Moreover, there have been proposed, as another method, a technique wherein a molten aluminum is infiltrated into a ceramic porous body by capillary pressure without giving a pressure after the wettability between a molten metal and a ceramic is improved by forming Mg3N2 on the surface of the ceramic body by utilizing a gas phase reaction in situ with evaporating Mg in nitrogen atmosphere (See JP-A-1-273659, JP-A-2-240227, or the like). This technique, however, has such problems that the infiltration speed of a molten metal is quite slow since Mg3N2 is coated in situ on the surface of the ceramic body, and that the adjustment of atmosphere for pressureless infiltration is very time-consuming. Additionally, there is such a problem that the reduction in the production cost of a composite material can not be attained since this technique requires the preparation of a porous ceramic body by firing a formed green ceramic body in advance, or the like.
As a related technique for solving the above described various problems, a method for production of an intermetallic compound matrix composite material is disclosed, in which self-combustion reaction by a metal powder mixed with a predetermined reinforcing material and aluminum (Al) molten metal is proceeded (See JP-A-2002-47519, for example). According to this method for production, as is shown in FIG. 2(a), molten aluminum (Al) 4 is infiltrated into pore 3 of a mixed material 2 comprising a dispersing material and a metal powder, which is filled in a reaction container 1 to induce a self-combustion reaction proceeds in-situ (on-the-spot), thereby the near-net shaping in the form of copied finished form of a composite material 5, such as an intermetallic compound matrix composite material having a high melting point, can be achieved under a low temperature and pressureless conditions, by an infiltration process that is completed in a very short time. Therefore, the amount of energy consumed in this method is markedly smaller as compared with conventional methods, thus leading to a method for producing a composite material with reduced producing cost.
However, since free control of the extraordinary large heat of reaction generated is not possible in a material synthesis process similar to the above described method for production utilizing a self-combustion reaction between elements (typically combustion synthesis reaction (SHS reaction)), this method is used in a synthesis of ceramic powder, or a compound having a high melting point (for example, a synthetic process of AlN and Si3N4 powder in nitrogen gas atmosphere using aluminum (Al) and silicon (Si) as start raw materials (direct nitriding method)), but in produce of a bulk body, it is known to be difficult to give a densified fine structure to the bulk body obtained due to pore formation by exothermic reaction, thus leading to difficulty of synthesis of a composite material having densified fine structure using the method. Therefore, it has been required in industrial world to provide a composite material having more densified fine structure than intermetallic compound matrix composite materials obtained by the above described method for production, and simultaneously having outstanding material characteristics resulting from the structure, and a method for production thereof.